Various imaging systems are used to form images on recording media. For example, computer-to-plate systems (also known as CTP systems) are used to form images on printing plates. A plurality of imaged printing plates is subsequently provided to a printing press where images from the printing plate are transferred to paper or other suitable surfaces. It is important that the plurality of images be accurately aligned with respect to one another to ensure an accurate registration among the images. It is important that each image be geometrically correct and free from distortion to ensure desired quality characteristics of the finished printed article. Geometric characteristics of an image include but are not limited to: a desired size of an image portion or a desired alignment of one image portion with another image portion.
The geometric accuracy of the images formed on a recording media is dependent on numerous factors. For example, images are formed on a recording media by mounting the media on a support and directing imaging beams towards the media to form the images thereupon. Scanning the recording media with the imaging beams during a plurality of scans typically forms the images. The positioning accuracy of the imaging beams with respect to the recording media impacts the geometric correctness of the formed images. Deviations in required positioning of the imaging beams during each scan can lead to imaging errors.
In order to reduce imaging errors, imaging systems are typically calibrated. Test images are typically formed on recording media and are analyzed to determine deviations. Deviations associated with a desired geometric characteristic of a test image are typically corrected by performing various adjustments in the imaging systems. The adjustments can be electronic or mechanical in nature. Analysis of the test images is typically performed on specialized and dedicated equipment that can include various image sensors. For example, CCD sensors can be used to capture various images of the test images and a controller can be used to analyze the captured images and determine positional information therefrom.
Specialized and dedicated calibration systems are costly and require regular calibration themselves to insure their integrity. Such systems are typically employed at the factory where the imaging systems are manufactured. Factory based calibration systems complicate the calibration of an imaging system in the field. For instance, test images would need to be made in the field and then shipped to another site for analysis. This increases the time required for calibration and increases the chances for imaging errors to occur.
Co-pending U.S. Patent Publication 2008/0299470 shows a system and method for changing the calibration of an imaging machine to adjust for geometric distortion while the machine is serving in the field. The machine addressed by U.S. Patent Publication 2008/0299470 comprises a single imaging head.
There remains a need for effective and practical methods and systems that permit the calibration of imaging machines with multiple imaging heads to correct geometric distortions of images formed by such multiple-head imaging machines.